Refer to FIG. 1 which is a block diagram of a conventional display device, a display device 9 includes a backlight module 90, a display panel 92, a backlight control module 94, a resistance unit 96 and a signal input module 98. The backlight module 90 includes a light-emitting diode (LED) array, and the backlight control module 94 includes a boost module 940 and a pulse width modulation (PWM) backlight controller 942.
The backlight module 90 is disposed at one side of the display panel 92 and provides the backlight source to the display panel 92. The PWM backlight controller 942 has a pin VCC, a pin DIM (i.e. a light dimming pin), a pin EN (i.e. an enable pin), a pin GND and a pin ISET. The pins VCC, DIM, EN and GND are the input pins of the PWM backlight controller 942, and the pin ISET is an output pin of the PWM backlight controller 942. The backlight module 90 is electrically connected to the boost module 940 and the PWM backlight controller 942 in the backlight control module 94. The boost module 940 is electrically connected to the PWM backlight controller 942. The resistance unit 96 is electrically connected between the pin ISET of the PWM backlight controller 942 and a ground end.
The pins VCC, DIM, EN and GND of the PWM backlight controller 942 are electrically connected to the signal input module 98. The pins VCC, DIM and EN are supplied with an external power source Vin, a PWM signal and a first voltage V1 respectively, and the pin GND is grounded. The external power source Vin is increased by the boost module 940 and then is supplied as power to the LED array in the backlight module 90 and the PWM backlight controller 942 in the backlight control module 94. The PWM signal is a basis that the backlight control module 94 adjusts the brightness. The first voltage V1 as an enable signal is fixed and used for being supplied to the backlight control module 94.
After the external power source Vin is increased via the boost module 940, the backlight control module 94 supplies power to the LED array in the backlight module 90 and through the PWM dimming technique, controls the brightness to the LED array. Specifically, the PWM dimming technique to adjust the brightness to the LED array is based on the duty cycle of the PWM signal, and the maximum of the output current Iout outputted by the pin ISET can be set through the design of the resistance unit 96.
FIG. 2 is a waveform diagram of an output current of the pulse width modulation backlight controller in FIG. 1. When the duty cycle of the PWM signal supplied to the pin DIM becomes greater, the brightness to the LED array in the backlight module 90 will become greater. In contrast, when the duty cycle of the PWM signal supplied to the pin DIM becomes smaller, the brightness to the LED array in the backlight module 90 will become smaller.
However, such a PWM dimming technique causes that flickers occur on the display device 9 two or three hundred times per second. In other words, the input current Iin outputted by the backlight control module 94 will change with a frequency of 200 or 300 hertz. It is not easy for human eyes to feel flickers occurring on the display device 9 because of the vision persistence, even though the human eyes view only thirty frames per second. Since the flickers may occur on the display device 9 more than 5 million times in eight hours in one day, this may cause a heavy burden to the human eyes and even cause eye diseases such as the computer vision syndrome. Moreover, when a camera or a video camera is used for capturing the images presented by the display device 9, lines may occur on captured images.
In order to remove the flickers, the conventional resolution is that the PWM backlight controller 942 in the backlight control module 94 is replaced by a current control chip having an inter-integrated circuit (I2C), thereby controlling the brightness to the display device through the linear current dimming manner. However, this solution will cause the more complicated circuit design within the display device and cause higher manufacture costs.